A review: Synthesis of carbon-based nano and micro materials by high temperature and high pressure

This review covers the production of solid carbonaceous materials at high temperatures (above 500 C) and high pressures. The review orders the high temperature/high pressure (HTHP) studies by their final product categories, namely carbon spheres, prolate spheroids (also known as ellipsoids and olivaries), nanotubes, and others such as diamonds, fullerenes, composites, and nanostars. The mechanisms as well as the properties of the products are discussed. In particular, the literature pertaining to the production of carbon ellipsoids has been collected for the first time. On one hand, the review concludes that, due to the existence of other conventional and more practical methods, the production of nanotubes and spheres via HTHP does not appear to be industrially feasible. On the other hand, using the HTHP method to produce olivary carbons and other new and exotic products seems attractive due to the absence of conventional methods for their production.